The application of optical communication technologies is extended to meet the needs of the amount of information transmission capacity with an explosive increase in the use of the Internet, etc. The development of optical communication techniques promotes introduction of fiber to home (FTTH), and accordingly, the low cost of a planar lightwave circuit (PLC) device becomes an important element of competitiveness.
Most conventional PLC devices are manufactured as silica-based PLC devices, but have many problems in terms of cost due to a high-temperature process and a complicated production process. In order to solve such problems, studies have been conducted to manufacture a polymer PLC device applicable to a low-temperature (<300° C.) process and a low-cost and mass-production process.
In a roll and plate (R&P) imprint process, a fine pattern is directly transferred by allowing a stamp with a fine structure to be physically contacted with a polymer layer. Hence, the R&P imprint process is simple, and thus mass-production is possible at low cost. Accordingly, the R&P imprint process has come into the spotlight as the most suitable process technique in manufacturing the polymer PLC device.
In the polymer PLC device manufactured by such a technique, an optical waveguide medium is formed inside the PLC device so that light passes through the optical waveguide. Therefore, an optical path as the optical waveguide medium should be very precisely formed to maintain the efficiency and performance of the polymer PLC device.
Accordingly, it is very important to develop a technique for manufacturing a large area stamp of a PLC device for an imprint process and a large area molding technique.
A conventional stamp of a PLC device is manufactured as a wafer-based stamp through photolithography and etching processes. In the technique for manufacturing the stamp through these processes, it is impossible to implement a branch pattern of 1 μm or less, and it is difficult to maintain uniform dimensional accuracy on the entire wafer. Therefore, it is difficult to implement a high-efficiency PLC device.
In order to solve such a problem, a high-precision stamp should be manufactured through electron beam exposure with high resolution. However, in manufacturing the stamp with a wafer size through the electron beam exposure, manufacturing cost is considerably increased, and it takes much time to perform the electron beam exposure.
Accordingly, there have been proposed methods for manufacturing a high-precision, large area stamp through an exposure technique and an imprint technique using a step & repeat method. However, the method for manufacturing the stamp using the step & repeat method requires equipment in which a precise stage system is built. Since a pattern is formed by the step & repeat method, it is difficult to equally maintain residual layers between unit patterns.
In addition, the size of the large area stamp is limited by an exposure system and imprint equipment using the step & repeat method.
If the stamp is manufactured through such processes, patterns are formed in the same shape.
The pattern formation of a polymer PLC device is performed by forming an under-clad channel through which light is waveguided by a thermal imprint method, using an embossing stamp, filling a core material in the under-clad channel, covering the core material with an upper-clad and then curing the core material through UV irradiation.
However, a gap portion of a micron or less exists in the pattern of the PLC device. When the pattern of the PLC device is manufactured by the thermal imprint method, the pattern of the PLC device may be broken or deformed due to sticking in a demolding process.
In a case where the core material is pressed while being covered with the upper-clad so as to manufacture the PLC device, the slab thickness is not only a factor for determining leakage of light but also a factor for maintaining adhesion between clad layers. Thus, it is very important to control the slab thickness.
In addition, it is very important to perform a refractive index control in the high-efficiency polymer PLC device. However, it is difficult to perform a precise refractive index control, using the curing method of the core material in the state in which the core material is covered with the upper-clad after the under-clad channel is formed.